Buggy code:
hbName . getChildren ( ) . addAll ( nameText , nameTF ) ; hbName . setAlignment ( Pos . CENTER ) ; hbName . setSpacing ( 75 ) ; hbPort . getChildren ( ) . addAll ( portText , portTFHS , randomBHS ) ; hbPort . setAlignment ( Pos . CENTER ) ; hbPort . setSpacing ( 75 ) ; hbAI . getChildren ( ) . addAll ( AIText , AICB ) ; hbAI . setAlignment ( Pos . CENTER ) ; hbAI . setSpacing ( 75 ) ; vbHOS . getChildren ( ) . addAll ( hbName , hbPort , hbAI , optionsHO , startHostingHO ) ; vbHOS . setAlignment ( Pos . CENTER ) ; vbHOS . setSpacing ( 50 ) ; bpHOS . setCenter ( vbHOS ) ; bpHOS . setBottom ( backHO ) ; Scene sceneHOS = new Scene ( bpHOS , 700 , 700 ) ; ObservableList livesoptions = FXCollections . observableArrayList ( "5" , "10" , "25" , "50" ) ; BorderPane bpGOS = new BorderPane ( ) ; VBox powerUpVB = new VBox ( ) ; HBox liveshb = new HBox ( ) ; HBox bottomhb = new HBox ( ) ; Text powerUpsText = new Text ( ( "Power<seq2seq4repair_space>Ups:<seq2seq4repair_space>" + "<seq2seq4repair_space>" ) ) ; powerUpsText . setFont ( new Font ( 20 ) ) ; CheckBox fastSlowCB = new CheckBox ( "Fast//Slow" ) ; CheckBox sheildCB = new CheckBox ( "Sheild<seq2seq4repair_space>" ) ; CheckBox multiCB = new CheckBox ( "Multi<seq2seq4repair_space>Ball" ) ; CheckBox bigSmallCB = new CheckBox ( "Big//Small<seq2seq4repair_space>" ) ; CheckBox magnetCB = new CheckBox ( "Magnet<seq2seq4repair_space>" ) ; CheckBox crazyCB = new CheckBox ( "CrazyBall<seq2seq4repair_space>" ) ; Text livesText = new Text ( "#<seq2seq4repair_space>of<seq2seq4repair_space>Lives:<seq2seq4repair_space>" ) ; livesText . setFont ( new Font ( 20 ) ) ; ComboBox livesCB = new ComboBox ( livesoptions ) ; Button okaybt = new Button ( "Okay" ) ; okaybt . setFont ( new Font ( 24 ) ) ; Button cancelbt = new Button ( "Cancel" ) ; cancelbt . setFont ( new Font ( 24 ) ) ; liveshb . getChildren ( ) . addAll ( livesText , livesCB ) ; liveshb . setAlignment ( Pos . CENTER ) ; bottomhb . getChildren ( ) . addAll ( okaybt , cancelbt ) ; bottomhb . setAlignment ( Pos . CENTER ) ; bottomhb . setSpacing ( 50 ) ; powerUpVB . getChildren ( ) . addAll ( liveshb , powerUpsText , fastSlowCB , sheildCB , multiCB , bigSmallCB , magnetCB , crazyCB , bottomhb ) ; powerUpVB . setAlignment ( Pos . CENTER ) ; powerUpVB . setSpacing ( 35 ) ; bpGOS . setCenter ( powerUpVB ) ; Scene sceneGOS = new Scene ( bpGOS , 700 , 700 ) ; BorderPane jsBP = new BorderPane ( ) ; VBox vbJS = new VBox ( ) ; HBox hbNameJS = new HBox ( ) ; HBox hbPortJS = new HBox ( ) ; HBox hbIP = new HBox ( ) ; Text nameTextJS = new Text ( "Name:<seq2seq4repair_space>" ) ; Text portTextJS = new Text ( "Port<seq2seq4repair_space>#:" ) ; Text ipText = new Text ( "IP<seq2seq4repair_space>address:" ) ; TextField nameTFJS = new TextField ( "<seq2seq4repair_space>" ) ; TextField portTFJS = new TextField ( "<seq2seq4repair_space>" ) ; TextField ipTF = new TextField ( "" ) ; Button backJS = new Button ( "Back" ) ; Button joinGameJS = new Button ( "Join<seq2seq4repair_space>Game" ) ; joinGameJS . setFont ( new Font ( 24 ) ) ; joinGameJS . setMaxWidth ( 300 ) ; hbNameJS . getChildren ( ) . addAll ( nameTextJS , nameTFJS ) ; hbNameJS . setAlignment ( Pos . CENTER ) ; hbNameJS . setSpacing ( 75 ) ; hbPortJS . getChildren ( ) . addAll ( portTextJS , portTFJS ) ; hbPortJS . setAlignment ( Pos . CENTER ) ; hbPortJS . setSpacing ( 10 ) ; hbIP . getChildren ( ) . addAll ( ipText , ipTF ) ; hbIP . setAlignment ( Pos . CENTER ) ; hbIP . setSpacing ( 75 ) ; vbJS . getChildren ( ) . addAll ( hbNameJS , hbPortJS , hbIP , joinGameJS ) ; vbJS . setAlignment ( Pos . CENTER ) ; vbJS . setSpacing ( 50 ) ; jsBP . setCenter ( vbJS ) ; jsBP . setBottom ( backJS ) ; <START_BUG> Scene jsScene = new Scene ( JSbp , 700 , 700 ) ; <END_BUG> quitBSM . setOnMouseClicked ( ( e ) -> System . exit ( 0 ) ) ; playBSM . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; optionsBSM . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( optionsScene ) ) ; backBOS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( startMScene ) ) ; hostBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneHOS ) ) ; backBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( startMScene ) ) ; playBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( jsScene ) ) ; backJS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; optionsHO . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneGOS ) ) ; backHO . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; okaybt . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneHOS ) ) ; randomBHS . setOnMouseClicked ( ( e ) -> { int portGen = ( ( int ) ( ( Math . random ( ) ) * 8847 ) ) ; String parsePortGen = Integer . toString ( portGen ) ; portTFHS . setText ( parsePortGen ) ; } ) ; primaryStage . setScene ( startMScene ) ; primaryStage . show ( ) ; primaryStage . setResizable ( false ) ; } public static void main ( String [ ] args ) { } }

Fix:
Scene jsScene = new Scene ( jsBP , 700 , 700 ) ;